Cutter for straight, helicoidal, and conical gear-teeth.



PATENTED OCT. l, 190'?.

L. BOISARD. GUTTER FOR STRAIGHT, HELIGOIDAL, AND CONIGAL GEAR TEETH.

APPLICATION FILED DBO. 21, 1905.

WITNESSES nur nnmns Urns co.. wAsm/vcmfv. n. c.

PATENTED OCT. 1, 1907.

l No.86'7,342. A

1.. BoIsARD. GUTTER FOR STRAIGHT, HBLIGOIDAL. AND GoNIoAL GEAR TEETH.

APPLIOATIONFILED DEC. 21. 1905.

INVENTOR i wim 55555 i PATENTED OCT. l, 1907.

3 SHEETS-SHEET 3 fag .9

INVENToR L. BOISARD. CUTTBRFOR STRAIGHT, HBLIGOIDAL, AND CONIGAL GEAR TEETH..

APPLICATION FILED DEO. 21. 1905.

y l2 is a perspective view of the cutter.

NITEI) STATES PATENT OFFICE.

LOUIS BOISARD, OF LYON, FRANCE.

Specification of Letters Patent.

Patented Oct. 1, 1907.

Application filed December 21,1905. Serial No. 292,774.

To all whom it may concern:

Be it known that I, Louis BoisAnD, a citizen of the French Republic, residing at Lyon, in France, have invented a certain new and useful Cutter for Straight, Helicoidal, and Oonical Gear-Teeth, of which the following is a specification.

This invention relates to an improved milling cutter for cutting gear teeth, its construction being such that the same cutter may be used for cutting the teeth of gears of different pitch between the two extreme pitches for which the cutter has been designed.

Since the cutter when used in the manner hereinafter referred to is capable of cutting teeth of profile suitable for true rolling contact at any pitch between the two said extreme pitches, it can be used for cutting beveled teeth provided the pitch near the apex and the pitch furthest from the apex do not respectively surpass the said extreme pitches. It can also be used for cutting parallel or beveled gear with helicoidal teeth. The cutter is produced by the superposition of two threads and the method of using it is the subject of another application for patent Serial Number 263,225.

In the annexed drawings Figures l to 8 are diagrams illustrative of the description of the method of constructing the cutter. Figs. 9 to 13 illustrate the manner of using the same. Fig. l is a diagram illustrating the development of the contour of the cutter but without illustrating the division of the thread of the cutter into separate cutting teeth. Fig. 2 is a diagram illustrating the development of a beveled wheel as a circular rack. Fig. 3 illustrates the cutting of a beveled wheel. Fig. 4 is a diagram of a section of the cutter thread illustrating the superposition of three threads. Fig. 5 is a development diagram illustrating the position of certain points on the primaries of superposed threads. Fig. 6 is a projection of these points into the plane of the diagram in Fig. 4. Fig. 7 is an enlarged view illustrating the superposition of the threads. Fig. 8 illustrates the cutter before the thread is divided into cutting teeth. Fig. 9 is a view illustrating the cutting of the teeth of a beveled wheel, the cutter being in the position corresponding to the cutting of the teeth where the pitch is smallest namely near the apex of the cone. Fig. l is a similar view illustrating the position of the cutter when the largest pitch is being cut. Fig. ll is an enlarged diagram of the tooth. Fig.

Fig. I3 is a sectional view illustrating the action of the cutter on a beveled wheel blank.

In order that this invention may be more easily understood I will first refer to the principles of the known method of cutting teeth by means of helicoidal cutters.

Straight and helicoidal gear teeth have been cut hitherto by means of milling cutters in the form of helices the pitch (p1) of which is, with regard to the pitch (p) of the gears to be cut, in the equation,-

where Cr is the angle contained by a tangential line perpendicular to a generator of the primary cylinder of the helical cutter and by a tangent to the helix at the intersection of this generator.

The operation of cutting a wheel of n teeth is performed by inclining the cutter at the angle Lr with re-` gard to the plane of the wheel and by revolving said cutter and wheel in such a manner that the wheel makes one revolution while the cutter makes n revolutions. The helical cutter may approximate to a rack adapted to cut teeth which are theoretically exact. If the rack, that is to say the cutter, has teeth with straight symmetrical sides, it cuts a wheel the teeth of which are in profile volute, and consequently a cutter with pitch p1 will impart the exact profile to any wheel with pitch p, for any number of teeth, provided, of course, that the cutter has either a suihcient number of convolutions to continue cutting action on the teeth until they are carried by the revolution of the blank out of the range of action of the cutting teeth or that a globular helical cutter is used. The angle Y of the tangent tothe thread can easily be determined ilI the diameter (d) at the point oi contact of the helical cutter is known, since l From this it follows that the pitch of the wheels which a helical cutter can produce is intimately connected with the angle of inclination of the cutter-thread, this angle being in turn subjectto the diameter of the helix. The same cutter can also cut helical gears with pitch P so that P Pi COS a P cos cos where /5 is the angle which the teeth of the helical Wheel make to the axis thereof. Finally the cutter can be used to cut any worm-wheel with a concave rim adapted to gear with a worm having the same diameter, pitch and axis direction as the helical cutter.

The helical cutters hitherto used have had a single thread of given pitch. My improved cutter is constructed in a different way. It consists of a thread of a given pitch on which is superposed a thread of another pitch so that the cutting part -is comprised only in that part which is common to the two threads. The constitution of this cutter is based on the following theory. A steel cylinder can, however, be turned in a lathe in such a manner as to give it a thread ol' pitch p1 adapted to cut a straight gear ol pitch p, when P=Pi COS ai and a thread ol pitch 19H1 can then be superposed on the I first thread, the second thread being adapted to cut a straight gear' of pitch pu. It is interesting to study the iorm Which the resultant thread (pitch p1) will take it' the primaries coincide.

Reference being made to the drawings tiled herewith in which Figs. l to S are illustrative ol the method ol lforming the cutter hereinal'ter more particularly eX- plained:-Given a cylinder oi diameter D (Fig. l), let there be traced thereon a helix E F G O l'l l l( ol pitch P1, and also a helix L M N O P Q R ol pitch Pn intersecting the lormer helix at O. Let these helices be developed by rolling the cylinder in plane, and two t straight lilies E F G O H l K and L M N O P Q R will be obtained. rhereupon let two straight lines be traced, parallel with E F G O H l K and equidistant from the latter, and a band or thread is obtained, ol lwidth l1=Q P1, Q being a given constant. ll a similar operation is perl'ormed with regard to the line L M N O P Q R, a second thread is obtained ol width ln==Q Pn. The part common to both threads is the parallelogram A D B C, having the sides A C and B D on the thread P1 and the sides A D and B C on the thread Pn. Now let a similar thread be traced, ol' the intermediate pitch Pk, with its central convolution passing through O. rlhe thickness el this thread will be 111=Q Pk and the two helices limiting the thread will pass through the points A and B bttt will only have these two points in common with the parallelogram A D 'l C. lt lollows that the sides ol' all similar threads with pitches varying l'rom P1 to Pn, and central convolutions passing through G, will pass through the points A and B, and the surl'ace common to all these threads will be the parallelogram A D B C, the sides ol which belong to the threads ol maximum and mini- Inum pitch P1 and Pn. Ol all these threads, let only the portion represented by the parallelogram A D B C be retained on the cylinder, and let this portion be in relief to an intinitely small extent, which enables it to produce its mark on a body with which it comes into contact;` also let d1, (Ik and an be the angles ol' inclination ot the helices ol pitches P1, P1( and P respectively, to a cross-section ol the cylinder. ll, thereupon, the cylinder, inclined at the angle Y1 is revolved in contact with a smooth-rimmed cylindrical Wheel oi the desired diameter, as in the case ol cutting cylindrical gear-wheels by means ol' a helicoidal cutter, said smooth-rimmed wheel being itsell rotated and connected with the cylinder by means ol' a suitable desmodromic movement, and il the cylinder is, while it revolves, moved parallelly to the axis el' the wheel, a series of rectangular markings will be produced on the latter, corresponding to spaces between teeth oi pitch p1, where P1=P1 COS Y1 and the Width Q P12-Q P1 COS a1 these markings being produced by the sides A C and B D belonging to the thread P1.

Il the Operation is repeated with the cylinder inclined at the angle 0/,1 with regard to another stneetlt rimini d wheel ol' suitable diameter. rectangular-tn rpitch p11 are obtained, where M22, Cos ltn and the width Q pnzil P11 COS (l'u1 plczPk CO5 LVI: and width Q pliz l)li (JOS l'Vlr these markings being produced by what remai ne nt' tin intermediate thread P11, that is to say the points fr and B only. Let thereupon a conical wheel be treated bjr means ol the cylinder, the pitches tor the teeth ttt be cut on said wheel being p1 at the major base and it, :tt the minor base. rl`he cylinder revolves in iront ttt' thi.- Wheel, the latter being kept in contact therewit lt ld' means oi a suitabledesmodromic movement, :tiel the cylinder, which advances parallel to a generator 's ;.t the same time moved, at a uniform rate, trom an a i ol inclination (X1 to an angle of inclination IVW l\` tlii f meansa series of trapeziums are traced on the enne. tet responding to the spaces between cnnieal teetlt the pitch of which varies from p1=P1 eos It, to nu: lj, et H11, the bases ol' the trapezitnns being etnial te and Q' p11-: Q P1! {lll respectively.

In the preceding remarks consideration bas been given to the points A and l given b v the intersect len ol all the threads considered solely with regard to their primaries, as il' the latter coincided. primaries oi the superposed threads do not eoinetde.

fln practice tlte l since all the threads have the same external diantet er and heights varying according to the pitch. Moreover, each intcrsectionol' the threads, at anydistanee troni tlte primaries, will give a series ol points, ot' whit-lt t and B maybe considered as the centers ol' the tienre tonsidering one thread oly pitch p1, (t ti e e t t, and 6), one, ier-example with straight sides tot' t lie salte ol clcarness, the exteritaldiameteroll the ent t errati-)fno thisthread will be D 77and the external development tri said cutter will be D. The primar)Y t/ nl' this thread will be such that the two pitchers pl and pl. These points liepreclnely in this cane on two straight linee r-r and al--r on which nre nlao all the pointe of intersection d b c s and It bfg. lf now a thread h b ij f intermediate pitch p* lie tnkeu it will be iound that the pointnoi inte'raec- ,tnn thereof with tht,` two previously considered threads fall on the lines l r and s' r, and that moreover, thevintcraection of the threads with the primary oi, for cxample, the large thrcnd'a b c c (line P in the diag-rain) coinciden with the point p-p. The linee 'l rand n' r therefore indicatethe '/.oneof the pointe of oscillation hereiuhefore referred to. lt therefore follow! thst tho cutter can .he determined by merely uperposing the two extreme threads a b c (and h mfg (Fig. 7), but in thin me projections h n a nnd g o s, which would be rornevcd by intermediate threads are left between the thread-intocii, these projections are removed and the cutter assumes n shape auch that the lines @-h and -g am straight.

A cutter for cutting conical gear-wheel: vby the method described can he produced in the following nmnner (not-'Fig 8). A deep thread of pitch Pl, with straight aides o b und e c, is cut by menne el n inthe in n steel cylinder nf diameter D (Fig. 8), so an to produce an endless crew of pitch Pl and primary diameter primar.) diameter, is always a function of the pitch.

li' lll is tho angle ef inclination of this thread to the primary cylinder, the screw, inclined at the unid ni'igli;A

Hl will he ndaptod to mesh with cylindrical wheels, meshing line of which corresponds to the slope of the surfuces a, l1 nudlc c nndrthe pitch oi which is apen-APW 'lhiu second th'read destroys in pnrt the thre'nd of pitch ll und produces, un it.wero, at oit-hor nido oitho point' t), where the central convolutionn of the two threads intersect cach other, a renultant thread onlnrgod nt its center und terminating in two pointe. Each section ot' this thread through n cylinder having the nume axis :is thc original cylinder will lntvo ne dcvolopuit-.nt u piuniiologtntn nonipnruhie lo the pnrullologrnni A D It t .-hown in Fig. l, nil pointu oi thiispnnillclogmm such un A und lt, coinciding with internoctionn M N,

(Fig. U). ily the second oporntion, thoroiorc, the endsensei lem crew in reduced to n re.` .Inez thrend ndnptmttn exactly mcnh: l"irntly, with tr'nr wheels oi pitch ll, when naid thrcnd is inclined nt nu :ingle nfl, nml tl-e. Ondly, with geur-wheels oi pitch [ln-ni, con 0'", thcu slid thread in inclined ut the :ingle Hl, corresponding to that of the thread of pitch P,

The lateral eurinceq of all threnfhi of pitch Pl intermediate to Pl und P.; produced in the nnnie manner with central convolutione pushing through O, intersect each other on tho same lines an the threads Pl und Pn, and these two linee M N und M N are all that romain of the lateral profiles oi' the threuds oiintcrmodinte pitch.- H the projecting part left by tho brises oi' the threads Pl and Puis so cut nwny soi to joinby u straight lino the dnd-points of said besos contained in each radial plane, a screw is obtained. having' the shape 'shown in Fig. 8 und ndnptcd lo nn-slH-flretlyl with gear-Wheels of pitch pl, ns ulrcndy cxpiuincd; secondly.,

with genr-wheeln of pitch pn, as has ehu heen oitpleinod;

thirdly with nny gem-wheels' oi pitch pk intermediate to pl and pn, if the thread is inclined nt the tingle all of the thread Pk, so that In this cano, however the lines M N nnd M Nl only touch the aides oi the teeth oi the wneel meshing with the screw. lf tite screw thus produced ia converted into n cutter, care being iukcn to retain the lince M N and M* N' as cutting edges, u cutter is obtained udeptod to be operated ou the principle oi the ordinnry helicoidal cuttci' und to cut geur-wheels. oi pitches varying from pl to pll, according-to the angle ll'l...\'k. ...lin at which the cutter is inclined. lhs cutter in, howover, too short, und cunuot comprise n suflicient number of threads oi euch pitch to envelop thocurvo of the teeth to be cut nnd to give thereto the desired -involuto. It itt, therefore, uocomtry to supplement this lack oi length by dinphicing the cutter in the direction oi its axis with u reciprocating movement oi such nmplitudo that the cutterthrcuds entirely envelop the tooth t0 be cut. This movement ia trnuxmittod to tho wheel by means oi dii'icrontnil geur included in tho mechanism which 'count-ctn thc'whcol with tin-.,cttttor, the wheel being ndvuncod und relnrded with un umplitude correr-:Winding lo thnt ol' tho nxinl dinpl-.tcouwut of the cutter.

IIt-it1 obvious thnt :t cutter of this kind een ho uned for cutting rionicnl gear-wliecls. l"or thin4 pro-porto it is nuflicient that tht.l cutter should receive, iu addition to the ntovemenlu imported to :t helicoidal coller l'or cutting cylindrical geur-wheels, tlniollouiug two :nlditional rnovementn:|.. lhc i'cciprrnr-.tting movement in tho direction Ioi its nxix, lwnd movoun-.ut hein" trunninittetl to the whocl in liu: nntnuci nlrendy des iin-d, as ahown by tht` dotted positions 2, Il for tht: cutter 'l in Fig. i). 2. A movenn-ut'by which tho :ingle oi inclimttion ol the cutter in chungt-d, ut u uniform tuto,

'from al to lin, imnmniug the tooth-pitch lo be pl ut the ntnjor wheel-huso und p ut the minor huso ne will be cen by computing fhc :inglel -of inclin-.tllou of tin` cutter inFigs. i) und It) rcspnctivcly; thin movement is controllod hy tho udvuuce ol' tincutter :dongr thu goncrntorn oi tht: cono :it thc hunt-r4 ol` tin: tei-th.

The system described lcen be uned for cutting ln-licoidnl bevel-gerne us well ne for c`uttiugr ntmight gouts. 

